I dont know this to be true but I've read that they may have had some production quality issues. And I agree, they do seem better than then generic ones especially with the bung fit.
Honestly though, I just had one develop a crack on the bottom and it leaked fermenting wort into my fermenchamber. The general consensus is that this is caused by soaking in PBW. I only do that because of stubborn kraussen that sometimes doesn't come off with the swirling washrag trick. So, given the lack of inventory on Better Bottles I have ordered a PET Big Mouth Bubbler. Those look like I wont have to soak in PBW since I can get my hand in the thing with a sponge.
Mine should arrive today in fact and I'll be dry hopping in it right off the bat.
I am interested in knowing what's happened to the Better Bottle supply though. If this Big Mouth Bubbler works out then it may not matter to me any more.